LOW PROFILE THRUST BEARINGS

Abstract: A hydrodynamic thrust bearing and method for manufacturing the same. The bearing includes spaced planar pads (132) supported on radially-extended beams (134). The beams are connected to a base ring (130) that is preferably circular. The radial beams support a circumferentially-central region of the pads, but permit deflection of the circumferential edges of the pads for wedge formation.

Description: LOW PROFILE THRUST BEARINGS Field of the Invention The present invention relates to hydrodynamic bearings and, more particularly, to hydrodynamic thrust bearing construction having an extremely low profile. Background of the Invention In most hydrodynamic bearings, a stationary bearing pad supports a rotating object such as a shaft via a pressurized fluid such as oil, air or water. U.S. Patent No. 3,107,955 to Trumpler discloses one example of a bearing having beam mounted bearing pads that displaces with a pivoting or swing-type motion about a center located in front of the pad surface. This bearing, like many prior art bearings, is based only on a two dimensional model of pad deflection. Consequently, optimum wedge formation is not achieved. In the Hall patent, U.S. No. 2,137,487, there is shown a hydrodynamic moveable pad bearing that develops its hydrodynamic wedge by sliding of its pad along spherical surfaces. In many cases the pad sticks and the corresponding wedge cannot be developed. In the Greene Patent, U.S. No. 3,930,691, the rocking is pro¬ vided by elastomers that are subject to contamination and deterioration. U.S. Patent 4,099,799 to Etsion discloses a non-unitary cantilever mounted resilient pad gas bearing. The disclosed bearing employs a pad mounted on a rec¬ tangular cantilever beam to produce a lubricating wedge between the pad face and the rotating shaft. Both thrust bearings and radial or journal bearings are disclosed. The present inventor's U.S. Patent No. 4,496,251 shows a pad that deflects with web-like liga¬ ments so that a wedge shaped film of lubricant is formed between the relatively moving parts. U.S. Patent 4,515,486 discloses hydrodynamic thrust and journal bearings comprising several bearing pads, each having a face member and a support member that are separated and bonded together by an elastomeric mate- rial. U.S. Patent No. 4,526,482 discloses hydrody¬ namic bearings that are primarily intended for process lubricated applications, i.e., the bearing is designed to work in a fluid. The hydrodynamic bearings are formed with a central section of the load carrying surface that is more compliant than the remainder of the bearings such that they will deflect under load and form a pressure pocket of fluid to carry high loads. It has also been noted, in Ide U.S. Patent No. 4,676,668, that bearing pads may be spaced from the sup¬ port member by at least one leg that provides flexibility in three directions. To provide flexibility in the plane of motion, the legs are angled inward to form a conical shape with the apex of the cone or point of intersection in front of the pad surface. Each leg has a section modulus that is relatively small in the direction of desired motion to permit compensation for misalignments. These teachings are applicable to both journal and thrust bearings. While the disclosure of this patent represents a significant advance in the art, it has some shortcom¬ ings. One such shortcoming is the rigidity of the sup¬ port structure and bearing pad, which inhibits deforma¬ tion of the pad surface. Further, the bearing construc¬ tion is not unitary. Additional background relating to this applica¬ tion may be gleaned by reviewing applicant's recently issued patents including U.S. Patent No. 5,255,984, which shows a variable characteristic thrust bearing. The bearing includes separately formed pads of various shapes and materials that are supported in a carrier. The car¬ rier is constructed such that the pads may be located in separate openings to vary the support characteristics. U.S. Patent No. 5,222,815 shows a variety of unitary bearings, including journal, thrust and combined radial and thrust bearings of the type having beam mounted bearing pads. The pads and support structure may be integrally formed as a single piece. Similarly, U.S. Patent No. 5,137,373 discloses thrust, radial and combined radial/thrust bearings in which the pads and support structure are integrally formed as a single piece. U.S. Patent No. 5,125,754 discloses thrust and journal bearings having a modular construction. In gen¬ eral, the bearings disclosed therein include separate pads or pad portions that are mounted in a separate carrier. Various pad and carrier configurations are dis- closed. U.S. Patent No. 5,102,236 discloses hydrody¬ namic thrust and radial bearings that each have a con¬ tinuous beam mounted shaft support surface. Summary of the Invention The present application is specifically directed to thrust bearings having a low axial profile. In the preferred embodiment, the bearing includes a low- profile thrust bearing for supporting a rotating shaft. The thrust bearing includes a base and a plurality of bearing pads circumferentially-spaced about the axis of the rotating shaft. Each of the pads has a substantially planar shaft support surface, radially inner and outer edges and side edges between the radially inner and outer edges and a supported surface below the shaft support surface. A plurality of radially extending beams con¬ nect the pads to the base. Each beam supports a portion of the supported surface that is spaced from the side edges of the pad. A variety of pad shapes and beam con- figurations can be employed. Brief Description of the Drawings The details of the invention will be described in connection with the accompanying drawings, in which: Fig. 1 is a top view of a low profile thrust bearing according to the present invention. Fig. 1A is a bottom view of the low profile thrust bearing of Fig. 1. Fig. IB is a cross-section of the bearing of Fig. 1 along the lines indicated in Fig. 1. Fig. IC is a cross-section of the bearing of Fig. 1 along the lines indicated in Fig. 1. Fig. ID is a cross-section of the bearing of Fig. 1 along the lines indicated in Fig. 1. Fig. IE is an upper perspective view showing the configuration of a bearing pad used in the bearing of Fig. 1. Fig. IF is a lower perspective view showing the configuration of a bearing pad used in the bearing of Fig. 1. Fig. 2 is a bottom view of another low profile thrust bearing according to the present invention. Fig. 2A is a cross-section of the bearing of Fig. 2 along the lines shown in Fig. 2. Fig. 3 is a bottom view of an alternate embodi- ent of the low profile thrust bearing according to the present invention. Fig. 3A is a cross-section of the bearing of Fig. 3 along the lines indicated in Fig. 3. Fig. 3B is another cross-section of the bearing of Fig. 3 along the lines indicated in Fig. 3. Detailed Description In describing the bearings of the present invention in an understandable way, it is helpful to describe the bearing structures as formed from a cylin¬ drical blank by providing grooves, slits, bores and other openings in the cylindrical blank. As noted below, this is sometimes a useful technique for manufacturing a prototype bearing. However, the reference to the cylindrical blank is primarily intended to assist understanding of the present invention. It should be noted that although many bearings of the present inven- tion could be manufactured from a cylindrical blank, it is not necessary that any of them be so manufactured. Indeed the bearings can be manufactured in numerous ways, some of which are discussed hereinafter. Figs. 1-3B illustrate embodiments of a low profile thrust bearing construction of the present invention. The currently preferred embodiment is shown in Figs. 1-1F. As shown in Fig. 1, the bearing includes a plurality of spaced bearing pads 132. Each of the bearing pads 132 includes a pad surface 132ps that is planar as can be appreciated from Figs. 1, IB, IC and 1A. The bearing further includes a radially inner support or base ring 1301 and a radially outer support or base ring 1300. In the currently preferred embodiment shown in Fig. 1, the inner and outer support rings 1301, 1300 have a circular configuration and are concentrically arranged. In the preferred embodiment, a plurality of circumferentially-spaced support spokes 136 extend between the radially inner support ring 1301 and the radially outer support ring 1300. These support spokes 136 provide rigidity to the bearing structure and maintain the alignment of the various portions of the thrust bearing. It will be appreciated by those skilled in the art, however, that the support spokes 136 are not essential in an embodiment such as that shown in Fig. 1 in which the radially extending beams 134 (discussed in greater detail below) extend between the inner and outer support rings. Thus, while the currently preferred embodiment shown in Figs. 1-1F includes such support spokes 136, they are not essential and could be elimi¬ nated if desired. As best shown in Figs. 1A, IC, ID and IF each of the bearing pads 132 is supported on a radially extending beam 134. In the preferred embodiment of Figs. 1-lF, the radially extending beam 134 extends between the inner support ring 1301 and the outer support ring 1300. Moreover, the support beam 134 extends continuously between the inner and outer support rings. Thus, the support beam 134 has the appearance of a single beam extending radially across the entire bearing pad 132 and connecting the bearing pad 132 to both the inner support ring 1301 and the outer support ring 1300. From a func- tional point of view, however, each of the beams 134 includes two radial beam portions: a radially inner beam portion 1341 that extends between the radially inner edge of the pad 132 and the inner support ring 1301 and a radially outer radial beam 1340 that extends between the radially outermost edge of the pad 132 and the outer support ring 1300. It should be understood, however, that it is not necessary that the radial beam 134 connect the pad 132 to both of the support rings 1301 and 1300. For example, the pad 132 could be connected only to the outer support ring 1300 by a radially outer beam portion such as 1340 so that the radially inner edge of the pads 132 is not rigidly connected to the support structure whereby the inner edge of the pad 132 may deflect down¬ ward to retain lubricant. As best shown in Figs. 1A and ID, the radial beam 134 of the preferred embodiment has a planar bottom surface that is adapted to be supported on a bearing support or similar rigid structure. By virtue of this configuration, the radial beam 134 provides an essen- tially rigid support for those portions of the pad 132 that it supports. As can be readily appreciated from both Figs. 1 and 1A, the radial beams 134 support a central region of the pads 132 that is spaced from either circumferential edge of the pads 132. Alternatively, the radial beams could have a triangular cross-section. The rectangular cross-section shown is preferred, however. In the preferred embodiment, shown best in Fig. 1A, the radial beams 134 are spaced closer to one circum- ferential edge than the other circumferential edge. As such, the bearing has different deflection characteris¬ tics depending on the direction of rotation and is intended to be a unidirectional bearing. Naturally, if it is desired to make a bidirectional bearing, the radial beam 134 should be spaced evenly between the circumfer¬ ential edges so as to provide a symmetrical support as discussed above in connection with other embodiments. Those portions of the pad 132 not supported on the substantially rigid radial beam 134 have flexibility that allows the pads to deflect under heavy loading to form a fluid film wedge. By virtue of the relatively rigid construction of the embodiment shown in Figs. 1-lF, this particular thrust bearing construction is intended for heavy load applications. The currently preferred applications are for use as a replacement for tapered land or similar bearings used in compressors and the like. Initial testing has shown that this bearing, although quite rigid, provides acceptable performance in such applications. The bearing may be made of a wide variety of plastic or metal materials although the currently pre¬ ferred embodiment is formed of bronze. To the extent the bearing can be formed of moldable materials, however, it should be noted that the bearing configuration shown in Figs. 1-lF includes no hidden openings. Thus, the bear¬ ing has a configuration that could be considered easily moldable, i.e., it can be molded in a simple two-piece mold not requiring any cam action. One important aspect of the bearing construc¬ tion shown in Figs. 1-lF is that it can be constructed with an extremely narrow profile. This is somewhat evident from Figs. IB-ID, however, it should be under¬ stood that the bearing can be formed with even a narrower profile by reducing the thickness of the pads and/or the thickness of the support rings 1301, 1300 and radial beams 134 and support spokes 136. Naturally, any change in the dimensions of the pads or the support structure will affect the rigidity of the overall bearing construc¬ tion. Accordingly, the deflection characteristics of the preferred configuration shown in Figs. 1-lF can be readily adjusted by changing the thickness of the various members and/or the material characteristics of the vari¬ ous members. Other modifications to the pad shape and sup¬ port structure are naturally possible. For example, the shape of the pad may be modified to achieve various deflection characteristics. For instance, the lower edge of the pads 132 could be tapered to increase inlet bend¬ ing formed with recesses to encourage lubricant channel¬ ling. In addition, as alluded to earlier, it is pos- sible to connect the pads 132 to the outer ring 134 only thus leaving the inner edge 132 of the pads unsupported. Such a construction is shown in Figs. 3-3B discussed below. Other possible modifications to pad shape are discussed below. Another possible modification of the preferred embodiment shown in Figs. 1-lF is shown in Figs. 2-2A. The low profile thrust bearings shown in these drawings is essentially the same as that shown in Figs. 1-lF with one significant exception: the inner and outer support rings 1301 and 1300 extend below the beams 134 such that the support rings 1301 and 1300 support the beams 134 above the base on which the bearing is mounted. As such, the beams 134 are supported for downward deflection under heavy loading and are not as rigid as in the preferred embodiment of Figs. 1-lF. This configuration provides yet another way to vary the deflection characteristics of the low profile thrust bearing of the present invention. Figs. 3-3B disclose an embodiment in which the radial beam 134 connects the pad 132 to the outer ring 1300, but does not connect the pad 132 to the inner ring 1301. The beam 134 extends only partially radially across the pads 132 such that an inner portion of the pads 132 is not rigidly supported by the beam 134. As such, the inner portion of the pad 132 is free to deflect downwardly. As mentioned previously, downward deflection of thrust bearing pads can be useful in retaining lubri¬ cant. Naturally, the radial extent of the beam 134 can be varied to alter the deflection characteristics of the bearing. An important aspect of the present invention is the disclosure of machinable bearing shapes, i.e., bear¬ ing shapes that can be produced by machining a piece of heavy walled tubing or similar cylindrical journal using standardly available machining techniques. Such bearings are characterized by the fact that they are formed from a piece of heavy walled tubing or similar cylindrical jour¬ nal through the provision of bores, slits and grooves. The advantage of such bearings is that it is easy to manufacture prototypes and to modify these prototypes after testing. Naturally, when the bearings are to be mass produced, using, for example, molding or casting techniques, different manufacturing considerations may dictate different shapes. It is important to recognize that changes in shape affect bearing performance. Another manufacturing consideration is ease of molding. Naturally, most of the bearing constructions of the present invention are capable of being molded by some molding technique. However, only certain shapes can be injection molded in a simple two-piece mold, i.e., a mold that does not include cams. Another advantage of the bearings of the present invention is that the bearings can be constructed with easily moldable shapes ,i.e., shapes that can be injection molded using a simple two- piece mold. An easily moldable shape generally is characterized by the absence of "hidden" cavities that require cams for molding. Easily moldable thrust bearings are character- ized by the fact that they can be molded with a single seam line such that, for example, when viewed only from the top and bottom, all surfaces are visible. All of the bearing constructions disclosed herein have, or can be readily configured to have, easily moldable shapes. For example, the low profile thrust bearings in Figs. 1-3B described above, have easily mold- able configurations. In the past, the pad shape of hydrodynamic bearings has been primarily dictated by manufacturing convenience. For a thrust bearing, this has tradition¬ ally meant sector shaped pads to maximize the area of support or — in the case of applicant's prior U.S. Patent No. 4,676,668 — circular pads for low cost manu¬ facture. For radial bearings, pads having a simple cylindrical section shape have been used. In many cases, such conventional pad shapes can be supported to obtain optimum results. However, the present inventor has dis¬ covered that important performance characteristics can be achieved by modifying conventional pad shapes. Conse¬ quently, the support structure can be simplified, and sometimes, even eliminated. Various modifications to traditional thrust pad shapes will be discussed hereinafter. It should be kept in mind that any of these modifications to the shape of the pad may be used in combination or alone. Also, the modifications can be easily adapted to pads having shapes other than the specific pad shapes illustrated. More¬ over, the pads may be symmetrically shaped to allow bidirectional operation or non-symmetrical to provide different operating conditions depending on the direction of rotation. The modified pad shapes discussed herein- after may be used in combination with any support struc¬ tures including those described in this application where appropriate or, when used in the proper combination, may eliminate the need for a deflecting support structure altogether. The first possible modification to the general pad shape is based on finite element analysis that has shown that, in some instances, increasing the length of the edge where the lubricant enters (the leading edge) can improve bearing performance. Specifically, lengthen¬ ing this edge allows more lubricant to be directed toward the pad center. To achieve this effect a radius cut may be formed on the pad surface to lengthen the leading edge. The cut may be formed either entirely through the pad or partially through the pad surface to provide a recess in the pad surface. Of course, the provision of such a radius cut decreases the load bearing surface of the pad. Thus, there is a trade off; more lubricant but less load bearing surface. Another possible modification to the basic pad shape involves tapering the leading edge of the bearing pad to increase inlet bending. This allows more lubri¬ cant to enter the shaft-pad space that increases the load carrying capability of the pad. Complex finite element analysis using computers can predict the amount of bend¬ ing needed to obtain optimum lubricant flow. The taper may be provided at each end to allow for bidirectional operation. If unidirectional operation is sufficient, only one edge, the leading edge, should be tapered. The basic pad shape may also be modified by providing rails on the side edges of the pads such that, under load, the pad deflects to form a channel that retains lubricant on the pad face and minimizes end or side leakage. As mentioned before, it is sometimes desirable to increase the inlet bending of the leading edge of a bearing pad. In addition to or instead of tapering the leading edge, a groove may be formed on the lower edge of the lower side of the pad proximate the leading edge to cause increased leading edge bending while maintaining a flatter surface. A final consideration in the design of specific pad shapes is the provision of bottom recesses on the pads. Specifically, the provision of bottom recesses can cause channeling and allow inlet bending. As mentioned before, the design of a pad shape for any particular application depends on the require- ents of that application. The foregoing structural modifications and considerations can be used alone or in combination.

Claims: What is Claimed is: 1. A one-piece thrust bearing for supporting a shaft that rotates about an axis, the bearing comprising: a plurality of circumferentially-spaced bearing pads (132) arranged around the axis, each of the bearing pads including a planar pad surface (132ps) , an inner radial edge, an outer radial edge and two circu ferentially- spaced edges extending between the radial edges, charac- terized in that the bearing comprises at least one circu- lar base ring (130) having an axis that is substantially coincident with the axis of rotation of the shaft; and a plurality of radial beams (134) , each of the radial beams extending between the circular base ring and one of the bearing pads. 2. A low-profile thrust bearing for supporting a rotating shaft, the thrust bearing comprising: a base (130) ; a plurality of bearing pads (132) circumferentially-spaced about the axis of the rotating shaft, each of the pads having a substantially planar shaft support surface (132ps) , radially inner and outer edges and side edges between the radially inner and outer edges and a supported surface below the shaft support surface; a plurality of radially extending beams (134) connecting the pads to the base, each beam supporting a portion of the supported surface that is spaced from the side edges of the pad. 3. A low-profile thrust bearing according to claim 2, in which the base comprises at least one circular base ring (130) having an axis substantially coincident with the axis of the rotating shaft. 4. A low-profile thrust bearing according to claim 3, in which the base comprises two radially-spaced circular base rings (1300, 1301) , one of the base rings being radially inward of the pads and the other base ring being radially outward of the pads. 5. A low-profile thrust bearing according to claim 4, in which the radially-extending beams (1341, 1340) extend radially between the radially inward base ring and the radially outward base ring. 6. A low-profile thrust bearing according to claim 4, further comprising a plurality of radial spokes (136) , each of the radial spokes being spaced from the pads and extending radially between the radially inward base ring and the radially outward base ring. 7. A low-profile thrust bearing according to claim 2, in which the radially-extending beams (1340) support a portion of the supported surface of the pads that is spaced from the radially inward edge of the pads. 8. A low-profile thrust bearing according to claim 4, in which the radially-extending beams (1340) are spaced from the radially inner edge of the pads and extend between the radially outer edge of the pads and the radially outer base ring. 9. A low-profile thrust bearing according to claim 4, in which the radially-extending beams (1340, 1341) having radial ends are supported by the circular base rings above the lower surface of the circular base rings. 10. A one-piece thrust bearing comprising: a plurality of circumferentially-spaced bearing pads (132) , each of the bearing pads including a planar pad surface (132ps) , opposed radially-extending circumferentially-spaced edges and inner and outer radial edges that are radially-spaced and extend between the circumferentially-spaced edges; a plurality of radial beams (134) , each radial beam being connected to a radial edge of a bearing pad and spaced from the radially-extending circumferentially- spaced edges of that bearing pad such that a longitudinal beam extends from at least one of the radially-spaced radial edges of each bearing pad; and two concentric circular base rings (1301, 1300) , each of the circular base rings being radially- spaced from one of the radial edges of the bearing pads, and the radial beams being connected to at least one of the circular base rings such that the radial beams con- nect the bearing pads to at least one of the circular base rings whereby the bearing pads are integrally con- nected to one another. 11. The bearing of claim 10, in which the radial beams have a triangular cross-section with the apex of the triangle directed away from the pad surface. 12. The bearing of claim 11, in which the pad has a triangular cross-section with the apex of the triangle being a aligned with the apex of the radial beams such that the pads and beams rest on the apex for tilting movement about the apex. 13. The bearing of claim 10, in which the radial beams have a substantially rectangular cross- section. 14. The bearing of claim 13, in which the circular base rings, the radial beams and the pads each have a maximum axial dimension as measured from the plane of the pad surface and wherein the maximum axial dimen- sion of the circular base rings exceeds the maximum axial dimension of the radial beams and the pads such that the base rings support the radial beams and the pads for axial deflection. 15. The bearing of claim 10, further compris- ing a plurality of spokes (136) extending radially between the circular base rings, each of the spokes being circumferentially-located between two bearing pads. 16. The bearing of claim 10, in which each of the bearing pads is connected to both of the circular base rings by a radially extending beam. 17. The bearing of claim 10, in which only the outer radial edge of each of the bearing pads is sup- ported by a radial beam and the inner radial edge is free to deflect downwardly.

Inventors: IDE RUSSELL D, IDE, RUSSELL, D.
Applicants: IDE RUSSELL D, IDE, RUSSELL, D.
Application year: 1994
Main classification: F16C17
IPC codes: F16C17